Wet developer system for electrostatic copier



Jan. 2, 1968 B. HOFFMAN ET AL 3,361,113

WET DEVELOPER SYSTEM FOR ELECTROSTATIC COPIER Filed July 15. 1964 5 Sheets-Sheet 1 ww NQQQQQQ Du 3, @Qwwmm: W2

\9 INVENTORS m K] LIONEL B. HOFFMA/V ALFRE KORAL Jan. 2, 1968 1.. B. HOFFMAN ET AL 3,361,113

WET DEVELOPER SYSTEM FOR ELECTROSTATIC COPIER Filed July 1s 1964 5 Sheets-Sheet 5 IT] l I I 4 I \9 I l I I \o x (Q m INVENTORS q? LIONEL B. HQFFM/I/V B HLFKED KORHL HTTORNE Y5 Jan. 2, 1968 HOFFMAN ET AL 3,361,113

WET DEVELOPER SYSTEM FOR ELECTROSTATIC COPIER Filed July 15, 1964 5 Sheets-Sheet 4 INVENTOR5 LIONEL 5 HOFFMAN FILF'RED KORQL BY Jan. 2, .1958 3,361,113

WET DEVELOPER SYSTEM FOR ELECTROSTATIC COPIER Filed July 15. 1964 L. B HOFFMAN ET AL 5 Sheets-Sheet 5 MEN INVENTORS LIONEL B. HUFFMA/V flLFRED KORHL ATTORNEYS United States Patent Ofiice 3,361,113 Patented Jan. 2, 1968 3,361,113 WET DEVELOPER SYSTEM FOR ELECTROSTATIC COPIER Lionel B. Hofiman, Hartsdale, and Alfred Kora], Flushing, N.Y., assignors to Saviu Business Machines Corporation, New York, N.Y., a corporation of New York Filed July 15, 1964, Ser. No. 382,806 9 Claims. (Cl. 118-637) ABSTRACT OF THE DISCLOSURE A wet developer system for an electrostatic copier in which a trough and an upper guide in spaced relationship form a channel-like restricted space extending transversely of the copy material path. Liquid developer is fed over one longitudinal edge of the trough through the space and out over the other longitudinal edge of the trough. The copy material is fed through the space in a direction countercurrent to the developer flow.

Our invention relates to a wet developer distribution system for an electrostatic copier and more particularly to a wet developer distribution system which is more efficient and more certain in operation than are developing systems of the prior art.

Of the many types of copying machines known in the prior art, there is the electrostatic copier in which a sheet of material having a photoconductive coating thereon receives an electrostatic charge and then is exposed to an image of the original to produce a latent electrostatic image of the original on the copy material. The copy material carrying the latent electrostatic image is passed through a developing zone in which it is brought into contact with particles of toner material which adhere to the copy material over the charged areas of the latent image. After passing through the developing station or zone the developed image is fixed.

In one system known in the prior art it has been suggested that a dry developer arrangement be employed. In such a system the developer, which is a mixture of carrier particles and toner particles, is brushed against the surface of the image carrying material as it passes through the developer zone. The electrostatic relationship of the toner and carrier particles to the charge on the copy material in such that toner particles are picked up by the charged areas of the material while the carrier particles are repelled and return to a tray or the like. The dry developer system has not proved entirely satisfactory owing to the fact that movement of the particles of toner and carrier cannot be closely controlled. The machine becomes dirty after a period of time in use and dirty copies are produced. Owing to this fact, the machine must be cleaned at relatively frequent intervals.

In an eifort to overcome the problems existing in dry developer systems, it has been suggested that wet developer systems be provided in which the developer is a suspension of toner particles in a suitable liquid carrier. In such a system, the copy material having the latent electrostatic image thereon is brought into contact with the liquid to cause the toner particles to adhere to the charged areas of the copy material.

Systems of the prior art which have attempted to em ploy a liquid developer have involved a number of defects. The operation of bringing the copy material into contact with the liquid developer creates a difficult problem of paper control. Owing to the tendency of the copy material to float on the surface of the developer, the material tends to crumple and fold resulting in jamming of the machine or at least in the destruction of a length of copy material. Moreover, it is necessary that the liquid bo brought into contact with the copy material over the entire surface thereof. Where the system is incorporated in a portable or semi-portable machine, it is further required that the machine be able to be transported from place to place without danger of spilling any appreciable quantity of the liquid developer. It is desirable that some distribution arrangement be provided for monitoring the liquid developer to determine when the relative proportion of toner is below a desired percentage. Moreover, it is desirable that a means be provided for indicating when the supply of developer is below a predetermined low level.

We have invented a wet developer distribution system which overcomes the disadvantages of developer systems of the prior art. Our system closely controls the movement of the copy material as it passes through the developer zone. It ensures contact of the developer with the copy material over the entire charged surface. It is provided with a simple and expeditious means for monitoring the toner content of the developer and has an improved arrangement for indicating that the developer supply has reached a predetermined low level.

One object of our invention is to provide a wet developer system for an electrostatic copier in which the copy material is controlled throughout its passage through the developer system.

Another object of our invention is to provide a wet developer system for an electrostatic copier which ensures contact of the developer with the entire surface of the image carrying copy material.

A further object of our invention is to provide a wet developer system for an electrostatic copying machine in which the system is provided with an extremely simple and expeditious arrangement for monitoring the toner content of the developer.

Still another object of our invention is to provide a wet developer system for an electrostatic copier having improved means for indicating that the developer has reached a predetermined low level.

Other and further objects of our invention will appear from the following description.

In general our invention contemplates the provision of a wet developer system for an electrostatic copier in which we flow liquid developer through a confined arcuate space in a direction countercurrent to the direction in which copy material carrying a latent electrostatic image passes through the space. We divert a portion of the pumped wet developer through the space in a translucent block between a light-responsive element and a light-producing element carried by the block. A float in the developer tank carries an element adapted to influence an external switch when the developer is below a predetermined low level.

In the accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

FIGURE 1 is a sectional view illustrating a form of our improved electrostatic copier having a dry developer system.

FIGURE 2 is a fragmentary sectional view of our improved electrostatic copier illustrating the original transport mechanism thereof.

FIGURE 3 is a side elevation of a wet developer system which can be employed in our improved electrostatic copier with parts broken away and with other parts shown in section.

FIGURE 4 is a fragmentary sectional view of the wet developer system shown in FIGURE 3.

FIGURE 5 is a side elevation of the toner replenishing system of the wet developer system shown in FIG- URE 3 with parts broken away and with other parts shown in section.

FIGURE 6 is a side elevation of a monitoring element of the toner replenishing system shown in FIGURE with a part broken away.

FIGURE 7 is a top plan view of the monitoring element shown in FIGURE 6 taken along the line 77 of FIGURE 6.

FIGURE 8 is a schematic view of one form of electrical control circuit which can be used on our improved electrostatic copier.

Referring now to FIGURES 1 and 2, we have shown one form of electrostatic copying machine indicated generally by the reference character 10 with which our developer system is adapted to be used. The machine 10 includes a bottom 12, a back 14, a top 16 and removable side panels, one panel 20 of which is shown in the drawings. The details of the machine with which our system can be used are shown more fully in the copending application of Charlap et al., Ser. No. 379,232, filed June 30, 1964. As is explained more fully therein, the machine includes an original transport system indicated generally by the reference character 26 disposed adjacent the front of the machine 10. The top 28 of this unit is provided with a push button (not shown) for turning the machine on and off, as well as a repeat copy mechanism indicated generally by the reference character 578 adapted to be set to make multiple copies in a manner pointed out more fully in the copending application.

As an original passes through the transport system 26, copy material 38 is drawn from a roll 40 carried by a shaft 42 supported in brackets 44 on the machine frame. That copy material 38 passes successively through a cut ting station indicated generally by the reference character 46, a corona system indicated generally by the reference character 48, an exposure station 50, a developing station 52 and a fixing system indicated generally by the reference character 54. Ultimately the developed copy moves outwardly through an opening 56 onto the surface of the top 16 at which it is accessible to the operator.

More specifically, when a copy is being made, a copy paper lower feed roll 58 is clutched to a shaft 60 to cause the paper to be drawn through the nip between the roll 58 and an upper feed roll 62 carried by a shaft 64. After passing through the cutter station 46, the copy material passes through the nip between a pair of feed rolls 66 and 68 carried by shafts 70 and 72. A pair of guide rolls 74 and 76 supported on shafts 78 and 80 carry the copy paper from the corona station 48 to the exposure station 50. As is known in the art, the copy material 38 carries a coating of photoconductive material such, for example, as zinc oxide or the like. As the length passes through the station 48, it is subjected to a potential between a corona discharge wire 82 disposed in a housing 84 and a ground roller 86 carried by a bracket 88. Having thus received a charge, the paper passes between a guide 90 on bracket 88 and a window 92 through which an image of the original to be copied is focused on the paper in a manner to be described.

Feed rolls 96 and 98 direct the copy material carrying the latent electrostatic image through the space 732 between a trough and an upper guide 730 to subject the material to a wet developer carrying particles of a suitable toner which adhere to the copy material over the charged areas thereof. After leaving the space 732 the copy material passes through the nip between squeeze rolls 742 and 744 carried by shafts 112 and 118 to the fixing station 54. The developer system will be described in more detail hereinafter.

Rolls 742 and 744 feed the developed copy material to the space between a pair of guides 114 and 116 which lead to a pair of feed rolls 11 8 and 120 carried by shafts 122 and 124. The copy material 38 then passes through the space between a guide 126 and a heater 128 which applies suflicient heat to the particles of toner carried by the sheet to fuse them to the sheet without at the same time scorching the sheet.

Guide rolls 130 and 132 carried by shafts 134 and 136 feed the copy material to an arcuate guide 138 which directs the leading edge of the sheet up into the nip between the roll 132 and a roll 140 carried by a shaft 142. The sheet is then fed upwardly between guides 144 and 146 to the nip between the roll 120 and a roll 148 carried by a shaft 151 As will be described in detail hereinbelow, when the original has passed through the original transport system 26, the length of material 38 being fed from the roll 48 has been cut to the length of the original. The cut sheet is :fed by rolls 128 and 148 to guides 152 and 154 which direct the sheet to the nip between rolls 156 and 158 carried by shafts 161) and 162. These terminal rollers 156 and 158 direct the sheet through opening 56 onto the upper surface of the top 16 where it is accessible to the operator.

Referring now to FIGURES 1 and 2, an original to be copied is fed to the system 26 by passing it into an opening 164 to the nip between feed rolls 166 and 168 carried by shafts 170 and 172. Guides 174 and 176 direct the original from rolls 166 and 168 to the nip between rolls 178 and 180 carried by shafts 182 and 184. Rolls 178 and 180 guide the original toward an exposure window 186 to the nip between rolls 188 and 190 carried by shafts 192 and 124. As the original passes by the window, light from a source 186 is directed onto its surface to reflect an image from the sheet through an opening 198 in a light reflector 200 along a path indicated by the dot-dash line in FIGURE 2.

As the leading edge of the original emerges from be tween rolls 188 and 190, it engages a guide 202 which directs the original to the nip between roll 190 and a roll 204 carried by a shaft 286. The sheet is then directed upwardly as viewed in the figures and is guided by guides 208 and 210 to the nip between roll 178 and a roll 212 carried by shaft 214.

Our original transport system comprises a bafile 216 adapted to be moved in a manner to be described between the full line position shown in FIGURE 2 and the broken line position. In the full line position of the baffle 216, it directs the original out through an opening 218 through which it is returned to the user. In the broken line position of the baffle, the leading edge of the original moves upwardly past the bafile to guides 220 and 222 which carry the original upwardly to a hip formed by roll 168 and a roll 224 carried by a shaft 226. When this occurs, a guide 228 on one of the walls of the opening 164 directs the original back to the nip between rolls 166 and 168 to cause the original to be recycled through the system 26. It will readily be apparent from the structure just described that the broken line position of the baflle 216 is that position it occupies when multiple copies of a single original are to be made.

We mount shafts 124, 136, 142 and 150 on a backdoor assembly comprising a door 230 secured to the back 14 of the machine by hinge pins 232. Any suitable means, such as a releasable catch 234 on the main frame, may engage a pin 236 on the door 238 to retain the door in its closed position. Inwardly extending flanges 238 on the door 230 support shafts 124, 136, 142 and 158, as Well as guides 126, 144 and 146. Side Walls 240 of the unit 26 carry shafts 170, 172, 182, 184, 192, 194, 206, 214 and 226, as well as the guides of the original transport mechanism. We removably mount the unit 26 on the main frame by means of hangers 231 engaging a bracket 233 on the main frame. Latches 235 engaging pins 237 on the assembly 26 hold it in position. The driving arrangement for the various rolls of the arrangement shown in FIGURE 1 is described in more detail in the copending Charlap et al. application.

In response to actuation of feeler 312 by the leading edge of an original passing through the system 26, roller 58 is clutched to the driving system to feed copy material through the cutter station 46. When the trailing edge of the original leaves the feeler 312 the roll 258 is unclutched and a cutting mechanism cuts the length of copy material to the exact size of the original in a manner described in the copending application of Oharlap et al. The corona wire 82 and the exposure lamp 196 remain energized until the trailing edge of the original leaves feeler 315.

Referring now to FIGURES 3 to 7, the developer system indicated generally by the reference character 702 of our machine includes a tank 704 adapted to contain a supply of a suitable liquid developer comprising a carrier having particles of toner material suspended therein. An inlet passage 706 at the top of the tank permits additional carrier to be poured into the tank in the event that the supply of carrier is depleted through evaporation or the like. A chamber 708 at one side of the tank to which fluid is admitted receives a float 710 carrying a magnet 712 adapted to influence a reed switch 714 outside the tank. It will readily be apparent that When the float 710 reaches a predetermined low level within the chamber 708, thus indicating that the supply of developer is at a predetermined low level, then the magnet 712 actuates switch 714 to light a lamp in a manner to be described hereinbelow to indicate that the supply of developer is too low.

We mount a pump 716 on the base 718 of the tank 704. A motor 720 is adapted to be energized to drive the pump to supply liquid developer to respective lines 722 and 724 connected to fittings leading to the impeller chamber 726 of the pump. A fitting 728 extending above the base 718 of the tank permits liquid to flow into the pump.

We provide our liquid developer system with a trough, indicated generally by the reference character 728, adapted'to be mounted on the top of the tank 704. This trough 728 receives an upper guide, indicated generally by the reference character 730, to provide a space 732 between the guide and the trough'through which copy paper carrying a latent electrostatic image can pass and be subjected to the action of the liquid developer.

We connect the tubing or pipe 722 to a fitting 734 leading into a distribution channel 736 extending from sideto-side of the trough. When pump 716 is being driven, developer supplied to the line 722 is fed up into the distribution channel and flows over an edge 738 of the channel into the space 732. It fills up this space 732 between the upper guide 730 and the trough 728 until the excess flows over an edge 740 at the front of the trough and returns to the tank 704. It will thus be apparent that the space 732 is supplied with developer liquid to a predetermined level.

A length of copy material passing through the machine is fed by rolls 98 and 96 into the space 732 and travels through the space and upwardly to squeeze rolls 742 and 744, the upper roll 742 of which is formed from rubber or the like and the lower roll of which is formed from metal. A wiper 746 is normally urged by a spring 748 into engagement with the roll 744 to remove moisture therefrom. From the rolls 742 and 744 the sheet of copy material passes to the section 54 which, in the liquid developer form of our machine, serves to dry the copy. It will readily be apparent that roller 742 may be carried by the driven shaft 112. It will be noted that we provide the upper guide with a plurality of ribs 750 on the underside thereof to facilitate passage of the copy material through the space 732.

In order to monitor the developer of our machine to ensure that the correct proportion of toner to developer is present, we connect the tube or pipe 724, which supplies liquid developer from the tank so long as pump 716 is driven, to one inlet 752 of a monitoring block 754 formed, for example, from a clear plastic resin. We form block 754 with a recess 756 for receiving a lamp 758 and with a recess 760 which receives a photocell 762. Passage 752 leads into a chamber 764 provided in the block between the chambers 756 and 760. It will readily be apparent that light from the lamp 758 passes through the walls defining the chamber 764 to the photocell 762.

6 In so doing, it also passes through the liquid developer within the chamber 764. Consequently, if the liquid developer is too light or in other words has too little toner therein, photocell 762 will develop an output signal at a predetermined level, which as will be described hereinafter actuates the replenishing assembly.

We provide the block 754 with a cover 766 to shield the block from extraneous light. Block 754 has an outlet passage 768 which we connect by a hose 770 to one inlet 772 of an injector or jet pump body 774. The inlet 772 leads to a passage 776 entering into a recess 778. A flow restricting passage 788 leads to a space 781. An outlet passage 782 is connected back to the tank by a tube 784. Cover plate 786 closes the recess 778 so that liquid coming in through fitting 772 travels through passage 776, through the space 778 and outwardly through passage 780, space 781 and outlet 782 back to the tank.

We form the body 774 with respective passages 788 and 790 leading into space 781 from opposite sides thereof. A tube 792 connects the passage 788 to the interior of the toner bottle 794 through the bottle cap 796. Conveniently, the bottle 794 may rest within the upper guide 730 with the level of toner in the bottle below passage 780. Another tube 798 connects the interior of the bottle 794 to the atmosphere through the cap. We connect the passage 790 to a normally open air valve assembly 800 by a tube 802. Valve 800 is adapted to be actuated in response to an electrical signal in a manner known to the art to close valve 800.

From the structure just described, it will readily be apparent that under normal conditions when the liquid within tank 704 contains suflicient toner, photocell 762 produces no effective output signal. At the same time valve 800 is open and the liquid passing through the injector body 774 merely is returned to the tank. If, however, the liquid developer becomes too light indicating that toner should be added, then photocell 762 produces an output signal, which in a manner to be described hereinafter is fed to the valve 800 to actuate the valve to close passage 790. When this occurs, a Venturi effect causes toner to be drawn from the bottle 794 into the passage 788 and thence to the space 781 wherein it mixes with the developer until the system has suflicient toner. It is to be understood, of course, that the operation just described can take place only if a signal has been produced by the counter mechanism to actuate switch 576 to indicate that the developer should be checked for quantity of toner.

Referring now to FIGURE 8, we have shown a form of electrical control circuit which may be used to control the operation of our copier. Respective fuses 804 and 806 connect our circuit to the terminals 808 and 810 of a suitable source of electrical power such, for example, as the usual volt 60 cycle alternating current. Respective rear interlock switches 812 ganged by a onnection 814 and lid interlock switches 816 ganged by a connection 818 connect the fuses 804 and 806 to on-olf power switches 820 gauged by a connection 822. Thus, the fuses 804 and 806 together with the switches 812, 816 and 820 connect terminals 808 and 810 to main control circuit conductors 824 and 826. It will readily be appreciated that in the normal condition of our circuit before the machine is set for operation, the rear door and lid are closed so that switches 812 and 816 are closed but the power switches 820 are open.

In order to condition our machine for operation, we close switches 820 to apply power to lines 824 and 826. We connect the heater 128 across lines 824 and 826 by thermostats 828. We connect the main drive motor 242, the pump motor 720 and a blower motor 830 in parallel across the lines 824 and 826 so that when the switches 820 close, the heater is energized and all the motors 242, 720 and 830 are energized.

A switch 832 is normally held in engagement with a contact 834 by the knife arm 380. We connect the solenoid winding 328 and the counter mechanism solenoid 540 in parallel between contact 834 and the arm 314 of the upper switch responsive to the feeler 312 first engaged by an original inserted in the machine. Before the original is inserted, arm 314 engages a contact 836. We connect a glow lamp 838 indicating insert between contact 836 and a contact 840 engaged by the arm 668 of the switch which indicates that no repeat copies are to be made. Ann 668 is connected to line 826. From the structure just described, it will be apparent that when the power switches 828 have been closed the circuit of lamp 838 is complete from line 824 through arm 832 and contact 834, through winding 328, through arm 314 and contact 836, through the lamp 838 and through contact 848 and arm 668 to conductor 826. Thus lamp 838 indicates that the machine is ready to receive an original.

With the machine in the condition just described, when a copy is to be made the original is inserted into the original transport mechanism to engage feeler 312 to move arm 314 out of engagement with contact 836 and into engagement with a contact 842. It will be understood that with lamp 838 in the circuit, winding 328 does not carry suflicient current to actuate the solenoid. When, however, arm 314 moves into engagement with contact 842, the winding is energized to pivot lever 334 to permit a switch arm 844 to engage a contact 846. The engagement of arm 844 with contact 846 energizes a relay winding 848 to close switches 858 and 852 to connect power from the fuses 884 and 886 to secondary control lines 854 and 856. In response to this operation, power is applied across the exposure lamps 858 and 868. At the same time, the high voltage power supply 862 is connected betwen line 824 and line 856 to apply power to the corona wires 82.

As the original travels through the original transport mechanism, it engages a second feeler 315 to operate a switch 864 having an arm 866 to move the arm out of engagement with a contact 868 and into engagement with a contact 878. This operation completes a circuit to winding 848 bypassing arm 844. Ultimately, the trailing edge of the original leaves the feeler 312 and arm 314 moves from contact 842 back to contact 836. Now, the solenoid 328 and the solenoid 548 are de-energized and arm 388 is permitted to operate the cutter mechanism. When this happens, arm 832 moves out of engagement with contact 834 and into engagement with a contact 872. As will be explained hereinbelow, this operation steps the multiple copy mechanism when the latter has been set to make more than one copy. Ultimately, the trailing edge of the original leaves the feeler 315 and arm 866 moves back into engagement with contact 868. Winding 848 is de-energized and the machine is set for the next copying operation.

As is pointed out more fully in the Charlap et al. application, we provide our machine with a counter mechanism for activating the monitoring system each time a predetermined number of copies have been made. The engagement of arm 314 with contact 842 applies power to a solenoid winding 548 of a counter mechanism 546 to step a earn 564 through one step. Each sixth step a follower 556 moves into a cam recess to permit a. switch 576 to close to energize the monitoring system.

The repeat copy mechanism shown in more detail in the Charlap et 'al. application comprises a shaft 642 adapted to be rotated to move a brush 788 to an intersegmental space between conductive segments 696 with the space corresponding to the number of copies to be made. When such a setting is made, an arm 668 of a switch positioned by shaft 642 moves into engagement with a contact 874 connected to one terminal of the resetting motor 678 of the repeat copy mechanism and to a terminal of a primary winding 876 connected to conductor 824. An indicating numeral illuminating lamp 668 is connected across a secondary winding 878 associated With winding 876 so as to be illuminated to indicate the number of copies to be made when the machine is set to make more than a single copy.

With the machine set for multiple copies, the cutter knife arm 380 moves to permit arm 832 to engage contact 874 to pulse motor 678 to initiate a movement thereof to bring the brush 788 into engagement with a segment 696 to provide a holding circuit for the motor while the brush 788 is in engagement with that segment. When the brush leaves the segment, the motor circuit is broken. The repeat operation continues until shaft 642 returns to its initial position whereat arm 668 is out of engagement with contact 874.

As has been explained hereinabove, each time a paper feeding operation begins, winding 548 is energized to move cam 564 through one step. After a predetermined number of steps of the cam, switch 576 closes to connect the toner replenishing circuit indicated generally by the reference character 888 across lines 824 'and 856. Circuit 888 comprises a diode 862 and a capacitor 884 forming a rectifier to provide a direct current potential on a conductor 886. A current limiting resistor 888 provides a suitable potential for illuminating the lamp 758 of the toner monitoring mechanism. A voltage regulating tube 898 regulates the voltage on conductor 886. As has also been explained hereinabove, light from the lamp 758 passes through the liquid developer toward the photocell 762 which we connect in series with a resistor 892 between line 824 and conductor 886. When the photocell 762 receives suflicient light, it conducts enough current to energize a relay winding 894 polarized by a diode 896 connected to the common terminal of voltage dividing resistors 898 and 988 connected between line 824 and line 886. When the winding 894 is energized, it closes a normally open switch 902 to energize the winding 984 of the valve assembly 888 to add toner to the liquid developer.

We connect switch 714 in series with a glow tube 986 between lines 824 and 826 so that when the supply of liquid developer reaches a predetermined low level, lamp 906 is illuminated to indicate that the supply of liquid developer must be replenished. A manually opeuable push button switch 988 permits relay 894 to be energized to add toner manually if desired.

In operation of a machine provided with our wet developer distribution system, with the lid closed and the machine plugged in, switches 828 are closed, for example, in response to the operation of a push button to energize heater 128, motors 242, 728 and 838 as well as the insert lamp 838. The original is fed into the system and passes therethrough one or more times depending on whether only a single copy or multiple copies are made. As is pointed out hereinabove, where multiple copies are made, lamp 668 rather than lamp 838 is illumi nated.

In response to actuation of feeler 312 by the leading edge of an original, roller 58 feeds a length of copy material 38 successively through the cutter station 46, the corona station 48 .and the exposure station 58. As this occurs and, as is pointed out more fully in the Charlap et al. application, a length of copy material is cut to the length of the original and it receives a latent electros-tatic image of the original to be copied. This length of copy material is fed by rolls 96 and 98 into the confined arcuate space 732 defined by the trough 728 and the upper guide 758. In the course of passage through this space, movement of the copy material is closely controlled. Motor 728 operates pump 716 to pump wet developer up through the channel 736 into the space 732 through which the developer flows countercurrent to the direction of movement of the material to ensure contact of the developer with the copy material over the entire surface thereof. The developer flows over the edge 748 back into the tank.

After leaving the space 732 the length of copy material passes through the nip between squeeze rolls 742 and 744 and excess developer is squeezed out of the material.

9 Wiper 746 removes excess liquid from the roll 744. The developed length of copy material then passes through the drying or fixing zone 54 and is delivered to the user through the opening 56.

Concomitantly with the operation of pumping developer into the space 732, pump 716 feeds developer through tube 724 and through the space 764 between the photocell 7'62 and the lamp 758. In this manner the toner content of the wet developer is continuously monitored. Each sixth copy, for example, cam 564 permits switch 576 to close to condition the toner adding system to add toner. The manner in which toner is added is described more fully in the copending Charlap et a1. application. In the event that the supply of developer in the tank 704 reaches a predetermined low level, float 710 positions magnet 712 to actuate reed switch 714 to energize lamp 906 to indicate that developer carrier should be added.

It will be seen that we have accomplished the objects of our invention. We have provided a Wet developer system wherein a reservoir of developer is maintained in the developing zone. Our system flows developer countercurrent to the direction of paper movement in the course of a developing operation to ensure that the latent image is completely exposed to the action of the developer. We provide an arrangement for monitoring toner content in the course of operation of the machine. Our machine is provided with means for indicating that the supply of developer is below a predetermined low level.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of our claims. It is further obvious that various changes may be made in details within the scope of our claims without departing from the spirit of our invention. It is, therefore, to be understood that our invention is not to be limited to the specific details shown and described.

Having thus described our invention, what we claim is:

1. In a liquid developer system for subjecting a length of copy material to the action of a liquid developer in a developing zone through which said length passes along a path, a trough elongated laterally of said path, said trough having longitudinal edges extending across said path and having side walls extending between said edges, a stationary upper guide elongated laterally of said path, said guide having a guide surface with a shape generally complementary to that of said trough, means mounting said guide and said trough in superposed relationship with said guide surface extending between said side walls and in closely spaced relationship thereto, said surface extending into said trough in relatively closely spaced relation thereto to form a confined generally arcuate space along said path and through which said length can pass, said space being laterally confined by said trough side walls, a distribution channel along one longitudinal edge of said trough between said sides, the other longitudinal edge of said trough forming a lip, a tank for holding a supply of liquid developer, said one edge and said lip being disposed above the low point of said trough and trough adapted to retain liquid in the space between said one edge and said lip, means for supplying liquid from said tank to said channel to flow liquid through said confined space and over said lip to said tank, and means for feeding a length of copy material along said path through said space.

2. In a system as in claim 1 in which said lip is below the level of said one edge.

3. In a system as in claim 1 in which said feeding means feeds said length in a direction from said lip to said channel.

4. In a liquid developer system for subjecting a length of copy material fed along a path to the action of a developer, a tank for holding a supply of liquid developer, a trough having a curved surface, an upper guide having a surface curved similarly to said trough surface, means mounting said trough and said guide on said tank with said surfaces adjacent each other to form a restricted channel-like space between said surfaces, said space extending from an entrance to an exit, said trough having edges extending transversely of said path at said entrance and at said exit, means for feeding a length of said copy material through said space from said entrance to said exit, means for flowing developer from said tank over said rear edge and through said space from said exit to said entrance and over said front edge to said tank, a float in said tank, signal means outside said tank and interacting magnetic means on said float and on said signal means responsive to the position of said float for indicating that said developer has reached a predetermined low level in said tank.

5. In a liquid developer system for subjecting a length of copy material fed along a path to the action of a developer, a tank for holding a supply of liquid developer, a trough having a curved surface, an upper guide having a surface curved similarly to said trough surface, means mounting said trough and said guide on said tank with said surfaces adjacent each other to form a restricted channel-like space between said surfaces, said space extending from an entrance to an exit, said trough having edges extending transversely of said path at said entrance and at said exit, means for feed-ing a length of said copy material through said space from said entrance to said exit, means for flowing developer from said tank over said rear edge and through said space from said exit to said entrance and over said front edge to said tank, a toner monitoring system and means for flowing developer from said tank through said monitoring system.

6. In a liquid developer system for subjecting a length of copy material fed along a path to the action of a developer, a tank for holding a supply of liquid developer, a trough having a curved surface, an upper guide having a surface curved similarly to said trough surface, means mounting said trough and said guide on said tank with said surfaces adjacent each other to form a restricted channel-like space between said surfaces, said space extending from an entrance to an exit, said trough having edges extending transversely of said path at said entrance and at said exit, means for feeding a length of said copy material through said space from said entrance to said exit, said copy material feeding means comprising a pair of squeeze rolls adjacent said exit, a wiper, means urging said wiper into engagement with one of said squeeze rolls and means for flowing developer from said tank over said rear edge and through said space from said exit to said entrance and over said front edge to said tank.

7. In a liquid developer system for subjecting a length of copy material fed along a path to the action of a developer, a tank for holding a supply of liquid developer, a trough having a curved surface, an upper guide having a surface curved similarly to said trough surface, means mounting said trough and said guide on said tank with said surfaces adjacent each other to form a restricted channel-like space between said surfaces, said space extending from an entrance to an exit, said trough having edges extending transversely of said path at said entrance and at said exit, means for feeding a length of said copy material through said space from said entrance to said exit, and means including a distribution channel along said rear edge for flowing developer from said tank over said rear edge and through said space from said exit to said entrance and over said front edge to said tank.

8. In a liquid developer system for subjecting a length of copy material fed along a path to the action of a developer, a tank for holding a supply of liquid developer, a trough having a curved surface, an upper guide having a surface curved similarly to said trough surface, means mounting said trough and said guide on said tank with said surfaces adjacent each other to form a restricted channel-like space between said surfaces, said space extending from an entrance to an exit, said trough having edges extending transversely of said path at said entrance and at said exit, means for feeding a length of said copy material through said space from said entrance to said exit, and means for flowing developer from said tank over said rear edge and through said space from said exit to said entrance and over said front edge to said tank.

9. In a liquid developer system for subjecting a length of copy material to a liquid developer, a trough having a curved surface, an upper guide having a surface curved similarly to said trough, means mounting said guide and said trough in spaced relationship with said surfaces adjacent each other to form a restricted channel-like space between said surfaces, means for feeding a length of copy material through said space and means for flowing developer through said space in a direction countercurrent to the direction of paper feeding, said upper guide confining said developer to the space therebelow.

References Cited UNITED STATES PATENTS 3,192,846 7/1965 Wright 95-94 3,284,224 11/1966 Lehmann 117-37 X 2,085,188 6/1937 Gerlach 95-94 2,393,678 1/1946 Graham 118-429 X 2,541,479 2/1951 Nadeau et al 118-429 X 2,632,330 3/1953 Marchment 73-313 3,249,088 5/1966 Ostensen 118-637 3,245,330 4/1966 Okishima 118-637 XR CHARLES A. WILLMUTH, Primary Examiner.

-P. FELDMAN, Assistant Examiner. 

